Acquisition of aerial imagery traces its history back to the Wright brothers, and is now commonly performed from satellite and space shuttle platforms in addition to aircraft.
While the earliest aerial imagery relied on conventional film technology, a variety of electronic sensors are now more commonly used. Some collect image data corresponding to specific visible, UV or IR frequency spectra (e.g., the MultiSpectral Scanner and Thematic Mapper used by the Landsat satellites). Others use wide band sensors. Still others use radar or laser systems (sometimes stereo) to sense topological features in 3 dimensions.
The quality of the imagery has also constantly improved. Some satellite systems are now capable of acquiring image and topological data having a resolution of less than a meter. Aircraft imagery, collected from lower altitudes, provides still greater resolution.
For expository convenience, the present invention is particularly illustrated in the context of a Digital Elevation Model (DEM). A DEM, essentially, is an “elevation map” of the earth (or part thereof). One popular DEM is maintained by the U.S. Geological Survey and details terrain elevations at regularly spaced intervals over most of the U.S. More sophisticated DEM databases are maintained for more demanding applications, and can consider details such as the earth's pseudo pear shape, in addition to more localized features. Resolution of sophisticated DEMs can get well below one meter cross-wise, and down to centimeters or less in actual elevation. DEMs—with their elevation data—are sometimes supplemented by albedo maps (sometimes termed texture maps, or reflectance maps) that detail, e.g., a grey scale value for each pixel in the image, conveying a photographic-like representation of an area.
There is a large body of patent literature that illustrates DEM systems and technology. For example:
U.S. Pat. No. 5,608,405 details a method of generating a Digital Elevation Model from the interference pattern resulting from two co-registered synthetic aperture radar images.
U.S. Pat. No. 5,926,581 discloses a technique for generating a Digital Elevation Model from two images of ground terrain, by reference to common features in the two images, and registration mapping functions that relate the images to a ground plane reference system.
U.S. Pat. Nos. 5,974,423, 6,023,278 and 6,177,943 disclose techniques by which a Digital Elevation Model can be transformed into polygonal models, thereby reducing storage requirements, and facilitating display in certain graphics display systems.
U.S. Pat. Nos. 5,995,681 and 5,550,937 detail methods for real-time updating of a Digital Elevation Model (or a reference image based thereon), and are particularly suited for applications in which the terrain being mapped is not static but is subject, e.g., to movement or destruction of mapped features. The disclosed arrangement iteratively cross-correlates new image data with the reference image, automatically adjusting the geometry model associated with the image sensor, thereby accurately co-registering the new image relative to the reference image. Areas of discrepancy can be quickly identified, and the DEM/reference image can be updated accordingly.
U.S. Pat. No. 6,150,972 details how interferometric synthetic aperture radar data can be used to generate a Digital Elevation Model.
From systems such as the foregoing, and others, a huge quantity of aerial imagery is constantly being collected. Management and coordination of the resulting large data sets is a growing problem.
In accordance with one aspect of the present invention, digital watermarking technology is employed to help track such imagery, and can also provide audit trail, serialization, anti-copying, and other benefits.
In accordance with another aspect of the invention, incoming imagery is automatically geo-referenced and combined with previously-collected data sets so as to facilitate generation of up-to-date DEMs and maps.
The foregoing and additional features and advantages of the present invention will be more readily apparent from the following detailed description.